***di.xml***

    <?xml version="1.0"?>
    <config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    
     <preference for="\Magento\Quote\Model\CouponManagement" type="Test\TestOverride\Model\CouponManagement" /> 
    
    </config>

**type="Test\TestOverride\Model\CouponManagement"**

**write your vendor and module name**

***CouponManagement.php***

***Test\TestOverride\Model\CouponManagement.php***